It is proposed to determine the repair of bleomycin-induced double-strand breaks in the DNA of E. coli cells. We will use the techniques already developed in this laboratory for the measurement of DNA double-strand breaks produced by ionizing radiations. The repair of other lesions made by bleomycin, such as alkali-labile bonds in DNA, will also be studied. We then hope to extend measurements to the DNA in mammalian cells. Here we will compare the lesions produced by bleomycin with those found in DNA treated in solution. We also plan to look for repair of double-stand breaks in mammalian cells. To characterize the mode of action of bleomycin on DNA, we will investigate bleomycin-DNA binding in the presence of suitable transition metal ions. We will also use EPR, NMR and optical spectroscopy to look at bleomycin-DNA-metal ion complexes.